The present invention generally relates to digital signal reproducing apparatuses, and more particularly to a digital signal reproducing apparatus which can satisfactorily reproduce digital signals recorded on a plurality of parallel tracks on a magnetic tape even when a relative positional difference exists in the track width direction between reproducing elements and a corresponding track.
Generally, when converting an audio signal into a digital signal and recording the digital signal on a magnetic tape by use of a stationary magnetic head, the total transmission rate in two channels is over 2 Mbits/sec when it is assumed that the audio signal converted into the digital signal by sampling the audio signal at a sampling frequency of over 44.1 kHz with 16 bits per channel. Hence, in order to stably record and reproduce such a digital signal, it is necessary to reduce the transmission rate per channel by increasing the number of tracks. For example, a compact type cassette tape is used as the magnetic tape and the number of tracks is selected to 20, and in a case where the recording is to be carried out in both forward and reverse directions, the track width of each of the tracks is selected to 65 .mu.m and the width of a guard band between two adjacent tracks is selected to 15 .mu.m.
The magnetic tape of the compact type cassette tape must be moved at a constant speed without deviations in the tape width direction, in order to reproduce signals from the plurality of pre-recorded tracks having the extremely small track width in the order of 65 .mu.m. Thus, a reproducing apparatus which is designed to play this type of magnetic tape is generally provided with high-precision tape guides on both sides of recording and reproducing heads, and one edge of the magnetic tape is guided along flanges of the tape guides so that the magnetic tape makes contact with the recording and reproducing heads at predetermined positions. The tape guides compensates for the deviation of the magnetic tape in the tape width direction for each cassette tape. On the other hand, a dual capstan mechanism employing a pair of capstans is provided on the reproducing apparatus to control the tape moving speed, the tape tension and the state of contact between the head and the magnetic tape to become constant. However, the established standard for the tape width of the magnetic tape of the compact type cassette is in a range of 3.81 mm-50 .mu.m to 3.81 mm+0. For this reason, the provision of the tape guides is insufficient to enable movement of the magnetic tape so that reproducing elements of the reproducing head accurately scan over corresponding tracks on the magnetic tape, which tracks have the extremely small track width in the order of 65 .mu.m.
Accordingly, in the conventional reproducing apparatus, one of the plurality of tracks on the magnetic tape is used as a control track, and a pair of control heads are arranged side-by-side in the track width direction of the control track. In this case, the tracking error is detected from a difference in outputs of the pair of control heads. The position of the head is displaced under control responsive to the detected tracking error so that the reproducing elements of the reproducing head accurately scan over the corresponding tracks on the magnetic tape.
There is another conventional reproducing apparatus provided with a light sensor at positions corresponding to the edges of the magnetic tape. According to this other conventional reproducing apparatus, variations in the lights reflected from the magnetic tape are detected, and the tape guides are displaced under control responsive to the detected light variations so as to compensate for the deviation of the magnetic tape in the tape width direction.
However, the conventional reproducing apparatuses described heretofore require tracking control means for displacing the reproducing head or the magnetic tape so that the reproducing elements of the reproducing head accurately scan over the corresponding tracks on the magnetic tape. When such tracking control means is provided on the reproducing apparatus, it becomes necessary to provide a detector, an actuator and the like exclusively for the tracking control, and there are disadvantages in that the reproducing apparatus becomes bulky and the expensive. Further, there is a disadvantage in that the tracking control cannot be carried out with respect to a resonance of the rotating system, mechanical resonance and the like, because the mechanical response of the actuator is to slow to enable the head to accurately follow the deviation of the magnetic tape in the tape width direction introduced by causes such as the resonance of the rotating system and the mechanical resonance.